based on Sotomayor's theorem [1]}. For \(\Delta =0\)  the points \(P_2\)  and \(P_3\)  collapse and \(P_1<P_2=P_3\) . Thus, there are two equilibrium points in the first quadrant. Those are \(P_1\)  and \(E_1=\left(1-A+M-u_1\right)/2\) .
